Decades of use with nearly four billion doses to humans preceded recent use with COVID patients. From the chapter ‘Ivermectin sends COVID to lockdown,’ in my book The Defeat Of COVID.
Ivermectin is on the World Health Organization (WHO) List of Essential Medicines and is approved by the US Food and Drug Administration (FDA). This well-tolerated but potent anti-parasitic medicine has been prescribed billions of times in its 36-year history against a wide range of parasites. It is a drug in the avermectin family, so named because those compounds are produced by the soil organism Streptomyces avermitilis. It has also been studied and used against a wide range of viruses especially over the last decade, and there is evidence of potent antiviral effects against Influenza A and over a dozen other viruses tested. 
In a meta-analysis of 63 studies of ivermectin versus COVID-19 in humans, 100% of these have shown positive results. Studies were from all continents except Antarctica. Considered individually, 29 of those studies were found to be statistically significant regarding use of ivermectin alone. Over the 63 studies in meta-analysis, pooled effects showed 69% improvement in early treatment, and prophylactic use showed 86% improvement. Of those studies in the meta-analysis that were peer-reviewed, overall improvement in early treatment was found to be 70% (64% in randomized controlled trials), and 86% of those in which ivermectin was used prophylactically showed improvement (84% in randomized controlled trials).
Mortality from COVID-19 over all time periods of delay in treatment was 76% improved over controls (69% in randomized controlled trials), whereas mortality was improved 84% in early treatment of COVID-19 (82% in randomized controlled trials). Forty studies were excluded from the meta-analysis for complicating factors or insufficient detail reported, and these also showed 100% positive results.
It is estimated that the likelihood of an ineffective treatment showing such positive results as the above results in the 63 studies in the meta-analysis to date is exceedingly small. That probability is estimated to be one in one trillion.  The overall results of the meta-analysis were not only found to be “overwhelmingly positive,” but also “very consistent, and very insensitive to potential selection criteria, effect extraction rules, and/or bias evaluation.” The data in the meta-analysis are as of date of this article, and are continually updated as new studies are reported.